Several demands are raised on cold work steel of high quality, including a proper hardness for the application, a high wear resistance, and a high toughness. For optimal tool performance both high wear resistance and good toughness are essential. VANADIS® 4 is a powder metallurgical cold work steel manufactured and marketed by the applicant, offering an extremely good combination of wear resistance and toughness for high performance tools. The steel has the following nominal composition in weight-%: 1.5 C, 1.0 Si, 0.4 Mn, 8.0 Cr, 1.5 Mo, 4.0 V, balance iron and unavoidable impurities. The steel is especially suitable for applications where adhesive wear and/or chipping are the dominating problems, i.e. with soft/adherent working materials such as austenitic stainless steel, mild carbon steel, aluminium, copper, etc. and also with thicker work materials. Typical examples of cold work tools, where the steel may be used are those which have been mentioned in the above preamble. Generally speaking, VANADIS® 4, which is subject of the Swedish patent No. 457 356, is characterised by good wear resistance, high pressure strength, good hardenability, very good toughness, very good dimension stability when subjected to heat treatment, and good tempering resistance; all said features being important features of a high performance cold work steel.
The applicant also has designed a steel WO 01/25499, having the following chemical composition in weight-%: 1.0-1.9 C, 0.5-2.0 Si, 0.1-1.5 Mn, 4.0-5.5 Cr, 2.5-4.0 (Mo+W/2), however max. 1.0 W, 2.0-4.5 (V+Nb/2), however max. 1.0 Nb, balance iron and impurities and having a microstructure, which in the hardened and tempered condition of the steel contains 5-12 vol-% MC-carbides, of which at least 50 vol-% have a size which is larger than 3 μm but smaller than 25 μm. This microstructure is obtained by spray-forming an ingot. The composition and microstructure affords the steel features which are suitable for rolls for cold rolling, including suitable toughness and wear resistance. Further, a high speed steel manufactured in a conventional way by ingot casting is disclosed in EP 0 630 984 A1. According to a described example, the steel contained 0.69 C, 0.80 Si, 0.30 Mn, 5.07 Cr, 4.03 Mo, 0.98 V, 0.041 N, balance iron. That steel, the microstructure of which also is shown in the patent document, after hardening and tempering contained totally 0.3 vol-% carbides of type M2C and M6C, and 0.8 vol-% MC-carbides. The latter ones had an essentially spherical shape and the large sizes which are typical for high vanadium steels manufactured in a conventional way comprising ingot casting. The steel is said to be suitable for “plastic working”.
The above mentioned steel VANADIS® 4 has been manufactured since about 15 years and has due to its excellent features reached a leading position on the market place for high performance cold work steels. It is now the objective of the applicant to offer a high performance cold work steel having still better toughness than VANADIS® 4 while other features are maintained or improved in comparison with VANADIS® 4. The field of use of the steel in principle is the same as for VANADIS® 4.